The present invention relates to a sliding or engaging element having at least two members. The elements are useful for example as sealing or bearing members. The mating or pairing of such sliding or friction members is known, especially in the form of axial friction ring seals or packing rings for armatures. The present invention requires that one of the members be formed of aluminum oxide and the other of silicon nitride, to give excellent wear and low friction high sealing characteristic.
GB-A No. 14 34 365 describes friction ring seals in which one of the two engaged members has a coating of boron carbide. This patent refers, for comparison, to sliding friction members made from hot-pressed silicon nitride in engagement with a counter-element of carbon. The silicon nitride/carbon combination of the "prior art" was evidently not considered to be particularly suitable.
EP-A- No. 0 118 056 describes the use of aluminum oxide and silicon nitride for the production of sealing components in a friction bearing, graphite being described as the material of the counter-element members.
Friction members of silicon nitride are also described in Japanese patent applications No. 50 223,34 020 and 16 0625, where they are described as being in engagement with counter-element members not further specified.
In the Dutch book, "Progress in Nitrogen Ceramics," 1983, pp 683 to 693, a sliding friction element pairing is also described in which both element members consist of sialon (silicon aluminum oxynitride).
In addition, a number of materials have been proposed for the seal plates of single-lever mixing faucets.
In the past, seal plates for single-lever mixing faucets were usually of aluminum oxide, sometimes mixed with, for example, zirconium oxide. Older publications, including, for example, DE-B No. 12 82 377; FR-A No. 14 54 755; DE-B No. 12 91 957; DE-A No. 28 34 146, relate to sliding friction element members and counter-element members of materials based on aluminum oxide. These proposals have certain disadvantages; in particular the known sliding friction element pairs have the disadvantage of excessively great static friction.
A more recent proposal by the applicant, however, provides in EPB No. 43 456 for a special mixture of ceramic material components for the achievement of an especially low percentage of areas in contact.
Although this proposal for the first time overcomes the prejudice that has heretofore existed that useful sealing action can be achieved only with a high percentage of areas in contact, it also contains certain practical disadvantages with respect to production. These disadvantages arise from the fact that, due to the extreme finess of the starting ceramic powders, in many cases the high power consumption causes the production costs to exceed economically acceptable levels for some uses. In more recent and not yet published patent applications, a surface treatment by etching or coating is proposed by the applicant to obtain sliding friction elements of lower friction coefficients. These methods, although leading to very good results with regard to sliding friction elements which have lower static friction, and also have an excellent sealing action, are also costly, so that the sliding friction elements made by these methods are not always practical. In Italian patent application No. 67 746-A/82, a sliding friction element has been proposed using members of hard materials having different properties, at least one of the plates consisting of silicon carbide.
One of the disadvantages of these proposals is that the proposed combination uses sliding friction element members of greater hardness or less smooth surface. The advantage is that the areas of contact between the two cooperating sliding friction elements will be reduced lowering friction therebetween. However to accomplish this entails relatively high costs due to the use of silicon carbide, and as a result of the different hardnesses of the sliding friction member, the harder sliding member acts almost as a surface-machining tool for the other, less hard sliding member, resulting in an undesirable alteration of the surface of the less hard sliding member.
Furthermore, in the case of a pairing of sliding member, e.g., a sealing disk pairing for a sanitary single-lever mixing faucet in which the one sealing disk consists of silicon carbide, and one sealing disk has a more complex geometry, the sealing disk with the more complex shape cannot be made from silicon carbide but must be made of aluminum oxide, for example. This is due to the known problems involved in the production of silicon carbide components. Furthermore, the sealing disk, which is especially subject to thermal shock, cannot be made from silicon carbide due to the more complicated shape of the sealing disk.
The existing disadvantages of silicon carbide are explained by the insufficient toughness of this relatively brittle material, so that chipping of components made from silicon carbide often occurs during manufacture, especially when they are made in more complex shape and are impacted during manufacture, e.g., when sandblasted, and when they are transported as bulk goods.
Lastly, DE-U No. 80 12 995 calls for silicon carbide or silicon nitride for the manufacture of different components in a wear-resistant armature for flowing substances. This document does not contain any proposal for the selection of the other elements in contact with the elements of silicon carbide and silicon nitride.
With respect to the known state of the art, the present invention has been directed to the problem of developing a sliding element whose paired or engaged members can be manufactured from ceramic materials known in themselves, without the need for expensive surface treatment processes. The sliding friction element members are to have a good sealing action and at the same time have low static friction coefficient in comparison to the known, uncoated ceramic elements made, for example, of aluminum oxide.